Method of hardening gelatine films and surfaces and resulting product



Patented July 5; 1932 UNITED STATES PATENT OFFICE FRANCIS CLARKE ATWOOD, OF NEWTONVILLE, MASSACHUSETTS, ASSIGN OR, BY MESNI? ASSIGNMENTS, '1.O TECHNIGOLOR, INC., 01' NEW YORK, N. Y A CORPORATION 01 DELAWARE METHOD OF HARDENING GELATINE FILMS AND SURFACES AND RESULTING PRODUCT No Drawing.

This invention relates to a'method for the preparation ofhardened surfaces of gelat ne or like material, particularly in associatlon with cellu'losic films, such as the celluloid films commonly used in photography and for motion picture reproductions,

The hardening of gelatinous films forwarious purposes has been known andpractlced in the prior'art by adding thereto certain oxidizing agents which act, in the course of time or in heated solutions of such agents, to stiffen and harden the gelatine. This hardening effect is accelerated b the action of light, more particularly t at of the ultra-violet portion of the spectrum.

. For some purposes, such procedure for hardening elatinous substances may be entirely satis actory. In other adaptations of materials so treated, however, as in the production of motion picture films in which the 4 requirements are exceedingly exacting, the rereproduction,-.for example one matrix filmcorresponding to the redsand a second matrix film corresponding to the complementary color thereto, or green,from which the reproduction is obtained by imbibition print-- ing and the blank transparent film upon which the final reproduction in colors is to be provided is printed from these matrix films. This is accomplished. by making superposed impressions upon the blank in red and green dye of appropriate color values, byrcontact with and imbibition from the socalled red and green matrix films, respectively. a

For such'pur oses, it is essential that the surface of the lm blank employed shall be readily wet by the dye and that it shall pref- Application. filed April 80,

1926. Serial No. 105,876.

erentially absorb or adsorb, during a relatively short contact period, substantially all of the dye contained upon the matrix film corresponding thereto, but that it shall-not be so porous as to permit spreading of the dye into other portions of the blank.- To

this end, it is desirable to harden the surface or outer layer of the gelatine coating, The term .harden is here employed to signify the alteration of the gelatine whereby it. is rendered more insoluble in water, and penetration and absorption of dye solutions and like coloring agents into the surface or through the outer portion of the gelatine layer is restricted, but without inhibiting the uniform wetting action of the dye in areas printed therewith. The hardening effect should be uniform over the treated surface and the film should be relatively inert with respect to dye substances, both chemically and physically. It is also important that the dye shall transfer uniformly from the matrix to the blank and thereafter remain in position and maintain its relative distribution thereover, as initially determined by the dye-wet portions of the matrix.

Blanks having surfaces or coatings of hardened gelatine are found to be best adapted to the conditions of transfer thus outlined, and are usually provided upon a backing of cellulosic material such as a celluloid film. In such cases, the gelatine surface or coating should be of uniform thickness and consistency with respect to its imbibition properties for example, and-should also be intimately associated with the celluloid backing towithstand subsequenthandling and treatment without separation therefrom.

The process of this invention includes preparing a fluid mixture or solution contain.- ing the gelatinous material to be used and a suitable hardening agent, extending the fluid into a continuous film or as a coating surface, rapidly drying the solution :to a

solid or firm consistency and then subjecting the gelatinous surfaceor film thus produced to a uniform elevated temperature (preferably above the normal atmospheric temperature but below such temperatures as may effeet a marked drying or dehydration of the priate strength and resiliency. To the surface of this film is applied a solution, also preferably uniform and transparent, con- "taining gelatine and a hardening agent such as potassium dichromate (in the proportion of approximately 5% of the gelatine used) usually with the addition of a small amount of an organic acid such as acetic preferably glacial (in an amount of about 3 drops per 100 cc. of the solution). The. solution is diluted to such consistency as will permit of spreading evenly and of uniformly wetting and adhering to the film. Uniform distribution and intimate association of the solution with the film are highly desirable, if not essential, for the best results in the hardening, printing and subsequent use of the film. This is best secured by careful control of the procedure involved, whether spraying, dipping, or other means, which are well known in the art. The coating thus applied is next allowed to dry, which should be efl'ected as rapidly as is consistent with the properties of the coated film, in order to avoidextensive interaction between the gelatine and the dichromate hardener. Reduction of the chromium of the dichromate from the chromic to chromous condition, for example, resulting in a greenish tinge before drying prevents its satisfactory use as an imbibition blank. The dry coated film is then subjected to a temperature appreciably above atmospheric, preferably 90-110 F., which is uniformly applied to all portions of the film surface either simultaneously to the whole, strip or progressively throughout its length, as by carrying the film through an extended heating chamber, by contact with heated rollers, by spreading out its full length in a constant temperature oven, or the like. It may also be conveniently effected by placing the loosely rolled film in a suitable container and setting the container in the heating chamber. Such heating treatment may be applied for 20 to 60 hours with the composition above described, or for a few hours only, as the case may be, depending in any given instance upon the proportions of hardening agent present, the character and composition of the gelatine used, and the degree and depth of the hardening action required. The surface or film is then washed out with water to remove the excess of hardening reagent and thoroughly dried.

Thus treated, the gelatine surface or coating is rendered harder and insoluble and hence, when employed as a blank for imbibition printing from photographic matrices and the like, manifests an absorption de ending upon the degree of hardening eflecte and produces, by a substantially complete dye transfer thereto, a transparent reproduction of accurate color. values, definition, afid registry. Moreover, the hardening efi'ect thus obtained is substantially uniform throughout the depth of the gelatine-coating or thickness of the gelatine film so treated.

The degree of hardening effected may be tested and controlled by withdrawing a sample, washing out excess reagent, drying thoroughly and immersing the hardened surface in a 5% solution of standardized pontacyl green S. F. (yellowish) which is the sodium salt of tetra methyl-diamino-diphenyl-B-hydroxy-naphthyl carbinol-disulphonic acid anhydride, color index No. 737, for a given period, sayfive seconds, and thereafter measuring the color density of the film. Thedepthior density of color penetration thus observed indicates the degree of hardening which has been effected in the gelatine surface. 7

It will be manifest that various modifications and adaptations of the invention may be made, both with respect to the specific conditions and procedures employed and by way of substitution of other reagents and materials withwhich it may be carried into practice. Such modifications and substitutions are, however, to be considered as comprehended by the above disclosure and included in the terms of the following claims.

I claim:

1. A process for preparing cellulosic films with a hardened gelatine surface, comprising applying to saidfilm a fluid coating of gelatine and a hardening agent containing soluble dichromate and an organic acid, rapidly drying the fluid coating thereon, and subjecting the thus coated film to an elevated temperature.

2. Aprocess for preparing cellulosic films with a hardened gelatine surface, comprising applying to said film a fluid coating of gelatine and a hardening agent containing 5% of a soluble dichromate based upon the weight of gelatine therein, together with an organic acid, effecting an intimate and uniform association of the fluid with the surface of the cellulosic film, rapidly drying the coating thus produced, and subjecting the coated film to an elevated temperature.

3. A process for preparing cellulosic films with a hardened gelatine surface,comprising applying to said film a fluid coating of gelatine containing a hardening agent and an organic acid, eflecting an intimate and uniform association of the fluid with the film surface, drying the same promptly and at low temperature, without appreciable reduction of the hardening agent, and subjecting the thus coated film to a temperature of 90 to 110 F. uniformly effective upon the film and coating.

4. A process for preparing hardened gelatine, comprising the steps of treating a gelatine composition with a hardening agent and with acetic acid, causing the same to set to a firm consistency, and subjecting the same to an elevated temperature.

'5. process for preparing hardened gelatine, comprising the steps of treating a gelatine composition with an organic acid and with a hardening agent,-'partially drying, and thereafter subjecting the same to an elevated temperature.

6. A process of preparing hardened gelatine, comprising forming a fluid mixture of gelatine, a hardening agent and acetic acid into the surface desired, drying the same,

and subjecting the dried film to an elevated temperature slightly above atmospheric.

7. A process of preparing hardened gelatine, comprising extending a fluid solution of gelatine, a 'dichromate hardening agent and acetic acid into the surface desired, drying and then subjecting the film to an elevated temperature.

8. A composition comprising an acidified 'gelatine, characterized by being of firm consistency uniformly hardened throughout the surface, and substantially without any free acid content.

Signed by me at Newtonville, Massachusett's, this 1st da of April, 1926.

, FRAN IS CLARKE ATWQOD. 

